In my first book, The Gone Fishin’ Portfolio, I made a confession that startled some readers…

I retired from the investment services industry while I was still in my early 40s, but many of my clients had not become financially independent. This was not because I advised them poorly. I dealt with my clients honestly and gave them the best advice and service I could.

Yet, in many ways, they operated at a disadvantage. Some had a poor understanding of investment fundamentals. Others found it impossible to commit to a long-term investment plan. Many were simply too emotional about the markets, running to cash at the first hint of danger.

Contrarian instincts are rare, too, I learned. Few people are emotionally stirred by low stock prices. But every time there was a correction, a crash, or financial panic, my Scottish blood would surge, my pulse would rise, I’d rub my hands together, and start buying.

My clients, on the other hand, often did just the opposite, sometimes because they were too nervous but often because they bought into the old chestnut that a good investor doesn’t buy into a market downturn.

“The trend is your friend,” they’d say. Or “Don’t try to catch a falling knife.” This is surely the conventional wisdom in some quarters, but it’s not particularly wise. Here’s why …

For the last several months, traders have obsessed over problems in the Eurozone and the strength (or perceived weakness) of the U.S. economy. Taking a decidedly downbeat view, the market had a pretty horrendous November. But sentiment can turn on a dime and stocks can put on a furious – and completely unexpected – rally.

If you don’t already own stocks, it’s tough to catch the train after it has left the station.

Yet many gurus, including growth-stock advocate William O’Neill and his widely read publication Investor’s Business Daily, often insist that you shouldn’t but a stock unless the market itself is in a confirmed uptrend.

That may make sense in theory, but it often fails in practice. For instance, on page one each day, that paper reports whether the market is in a confirmed uptrend or downtrend. (And sometimes hedges, using language such as “Uptrend Under Pressure.”)

As we all know, this has been a volatile year for the market with the major indices bouncing up and down repeatedly. But you could hardly have chosen a worse strategy than to wait until the market was in a confirmed uptrend before buying. All that meant was that you bought into every short-term spike and then hit your trailing stops over and over again. (It must feel like banging your head against the wall.)

The Oxford Club has hit a number of its stops this year, too, sometimes protecting profits, other times protecting principal. But by buying great companies when the market was under pressure, we ended up with a lot of attractive entry points and plenty of both realized and unrealized profits.

True, if stocks go into a secular bear market, you can end with losses no matter how well you timed your entry points. However, you can never know whether a market drop is merely a correction or something more ominous until you are looking in the rear-view mirror.

You have to stick your neck out occasionally, pick your spots and buy stocks. If you don’t, what are you going to do? Buy bonds yielding 2.5 percent? Hold a money market paying less than one-tenth of one percent? It’s tough to beat inflation or meet your financial goals that way.

Let me make one thing clear, however. It’s most definitely a mistake to buy a troubled company that’s in a downtrend, no matter which way the broad market is heading. (That only works for those with exceptionally long time horizons – and often not even then.) But buying great companies when the broad market is a downtrend gives you a chance to obtain good prices on fine long-term investments and take advantage of tradable short-term rallies, too.

The next two months are traditionally one of the strongest periods for the stock market. No one can say, of course, whether that tradition will hold. But it’s a reasonable strategy to buy great companies when the market is down.

If your goal is to sell high, you have to start by buying low. And market corrections – like the one we’ve seen lately – give you an excellent opportunity to do just that.